Carbon black refractory system

ABSTRACT

A refractory system for a reactor for producing carbon black. The system comprises a plurality of refractory bricks having an elongate axis arranged to provide at least one path through which a gas can flow. The path extends substantially perpendicular to the elongate axis and a plurality of the refractory bricks present a cross-sectional aspect to the gas flow which decreases, in the downstream direction, from a maximum aspect to reduce dead regions in gas flow adjacent the refractory bricks.

This application is a division of application Ser. No. 08/175,579 filedDec. 30, 1993, now U.S. Pat. No. 5,499,477.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refractory system for use in reactorsfor producing carbon black.

2. Description of the Prior Art

It is known to produce carbon black in commercial quantities by crackinga hydrocarbon feedstock material, such as natural gas (containing amixture of one or more of methane, ethane, propane and butane gases),refinery bottoms, etc. to obtain carbon black and hydrogen gas. Whenmethane is employed, the reaction may be represented by the equation:

    CH.sub.4 →C+2H.sub.2 +(trace quantities of aromatic compounds, illuminant gases and uncracked methane)

Known commercial processes for cracking methane to form carbon black,commonly referred to as `thermal black`, comprise the steps of heating acheckerwork of refractory bricks in a reactor to a temperature of about2700° F. and then passing the feedstock methane through the checkerworkin an essentially oxygen free environment. During the reaction, themethane is cracked into a mixture of thermal black, hydrogen gas andtrace amounts of undesired byproducts. To drive the endothermic crackingprocess, energy (heat) is removed from the refractory bricks during thecracking operation, thereby reducing the temperature of the bricks. Whenthe temperature of the refractory bricks is lowered to about 1200° F.,the reaction must be terminated to allow the refractory bricks to bereheated to the desired temperature.

Problems exist with the known processes in that some thermal blackaccumulates on the refractory brick and degrades the thermal transferprocess, both during the heating of the bricks and during the crackingof the methane. It has been determined that this degradation reduces theefficiency of the thermal black production process, reducing the yieldand increasing the cost of the final product. A further problem existswith known processes in that, at the operating temperatures within thethermal black reactor, the accumulated thermal black eventually reactswith the generally silica-based material of the refractory brickscausing erosion and/or breakdown of the bricks. This breakdownnecessitates that the reactors be `re-bricked` sooner, and thus moreoften, than would otherwise be the case. Moreover, rebricking requiresthe reactor to be shut down for relatively long periods of time andincurring a significant cost for the labour and materials to effect therebricking. Further, as the refractory bricks erode and breakdown, theeroded refractory material tends to contaminate, and thus lower thequality of, the thermal black final product.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel refractorysystem for producing carbon black which obviates or mitigates at leastone of the above-mentioned problems of the prior art.

It is a further object of the present invention to provide a novelprocess of producing carbon black.

According to one aspect of the present invention, there is provided arefractory system for a reactor for producing carbon black, the systemcomprising: a plurality of refractory bricks having an elongate axisarranged to provide at least one path through which a gas can flow, theat least one path extending substantially perpendicular to the elongateaxes and the plurality of refractory bricks being shaped to reduce deadregions in the gas flow adjacent the refractory bricks.

According to another aspect of the present invention, there is provideda process of producing carbon black from a gaseous hydrocarbon feedstockcomprising the steps of:

(i) introducing a gas flow comprising the feedstock to a refractorysystem comprising a plurality of refractory bricks;

(ii) arranging the refractory bricks to present a cross-sectional aspectto the gas flow,

(iii) heating the refractory system to a predefined first operatingtemperature;

(iv) decreasing the aspect in the direction of the gas flow;

(v) producing a carbon aerosol comprising carbon black; and

(vi) separating the carbon black from the carbon aerosol.

It will be apparant to those of skill in the art that the order ofcertain Steps in the present process is not particularly restricted. Forexample, Steps (iii) and (iv) may be reversed without departing from thescope of the present process.

In a preferred embodiment, the present process comprising the furtherstep of: (vii) stopping the gas flow when the temperature of therefractory system drops to a predefined second operating temperature. Inthis embodiment, it is most preferred if Steps (iii) through (vii) arerepeated in a cyclical fashion.

As used throughout this specification, the term "predefined firstoperating temperature" is meant to encompass the temperature to whichthe bricks in the refractory system are heated to effect production of acarbon aerosol comprising carbon black. Practically this translates to atemperature of at least about 2400° F., preferably a temperature in therange of from about 2400° to about 2950° F., more preferably in therange of from about 2500° to about 2900° F., most preferably in therange of from about 2600° to about 2800° F.

As used throughout this specification, the term "predefined secondoperating temperature" is meant to encompass the temperature to whichthe bricks in the refractory system are cooled sufficiently such thatproduction of the carbon aerosol comprising carbon black is complete andthe bricks must be reheated. Practically this translates to atemperature of less than about 1500° F., preferably a temperature in therange of from about 1000° to about 1500° F., more preferably in therange of from about 1000° to about 1400° F., most preferably in therange of from about 1100° to about 1300° F.

In a preferred embodiment of the present process, after the carbon blackis separated from the carbon aerosol (i.e. Step (vi)), the latter isrecycled to the heating step (i.e. Step (iii)) to improve the overallefficiency of the process

The term "carbon black", as used throughout this specification is meantto encompass artificially prepared carbon or charcoal. Non-limitingexamples of carbon black include thermal black, furnace black, lampblack and the like. The present invention is particularly suited to asystem for the production of thermal black.

Preferably, the refractory bricks are arranged in at least first andsecond courses, the elongate axes of the refractory bricks of eachcourse being arranged perpendicular to the elongate axis of therefractory bricks of the course above or below. Also preferably, therefractory bricks in one course include means to engage the refractorybricks of the course above or below and the means to engage ispreferably a groove, or half-groove, sized and shaped to engage therefractory bricks.

In a presently preferred aspect of the invention, the refractory bricksare circular in cross-section, although elliptical and tear-drop andother shaped embodiments are also contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates a prior art carbon black reactor;

FIG. 2 illustrates a representation of a gas flow past a prior artwedge-shaped refractory brick;

FIGS. 3a through 3l illustrate component refractory bricks of oneembodiment of the present invention;

FIG. 4 illustrates a representation of a gas flow past a refractorybrick according to the present invention;

FIGS. 5a and 5b illustrates portions of courses of refractory brickslaid in a reactor in accordance with the present invention;

FIG. 6 illustrates a portion of a refractory system constructed inaccordance with the present invention;

FIG. 7 illustrates a section of FIG. 6, taken along line 7--7;

FIG. 8 illustrates a top view of a section of a refractory systemconstructed in accordance with the present invention in a reactor;

FIG. 9 illustrates a sectioned side view of the reactor of FIG. 8;

FIG. 10 illustrates a cross section through an elliptical refractorybrick in accordance with the present invention;

FIG. 11 illustrates a cross section through a tear-drop shapedrefractory brick in accordance with the present invention; and

FIG. 12 illustrates a cross section through a multi-side shaped brick inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a prior art thermal black reactor 10. Reactor 10comprises a vertical cylindrical body 20 which is lined with arefractory material 22. The interior of reactor 10 surrounds acheckerwork 24 of wedge-shaped refractory bricks 28 which define aseries of tortuous passages 32. Gases flow through passages 32 from apair of ports 35,36 at the top of reactor 10, to a series of exit ports40 at the bottom of reactor 10.

Reactor 10 operates in two cycles, a heat cycle and a make cycle. In theheat cycle, combustion air enters reactor 10 through entry port 35 and asuitable fuel enters reactor 10 through entry port 36. The resultingfuel-air mixture is combusted to heat refractory bricks 28 to a desiredtemperature. Typically, thermal black reactors are operated in pairswith one reactor in a make cycle while the other is in its heat cycle.In such a case, the hydrogen gas produced by the make cycle reactor isused as the heating fuel in the heat cycle reactor and the cycles of thetwo reactors are alternated regularly. The waste products from thecombustion of the fuel in the heat cycle exits through the ports 40 atthe bottom of the reactor and may be directed to an incinerator (notshown) through a control gate 42.

Once refractory bricks 28 have reached the desired temperature (2700°F., for example), the supply of combustion air and fuel is terminatedand methane feedstock enters reactor 10 through entry port 36. As themethane travels through passages 32 defined by the wedge-shapedrefractory bricks, it is cracked into a `carbon aerosol`, which is agaseous mixture of hydrogen and the thermal black. The mixture of carbonaerosol and trace quantities of aromatic compounds, illuminant gases anduncracked methane exits the bottom of the reactor through exit ports 40and passes through one or more water sprays 46 which cool the mixture.The mixture is directed through a control gate 50 to a `baghouse` (notshown) wherein the thermal black (and any other solids) are separatedfrom the remainder of the gaseous components of the mixture.

Over the course of time, some thermal black accumulates on at leastportions of the refractory bricks. As previously mentioned, this thermalblack accumulation degrades the efficiency of the heat transfer to andfrom the refractory brick (essentially acting as an insulator). Thisdegradation results in a reduced yield of thermal black as some thermalblack remains in the reactor after completion of the make cycle andprincipally because the cracking reaction is not as efficient due to thereduced thermal transfer from the refractory brick to the hydrocarbonfeedstock.

Further, as mentioned above, at the operating temperature of thereactor, the accumulated thermal black reacts with the silica-basedrefractory material to erode and degrade the bricks, and also results incontamination of the thermal black final product which is recovered inthe baghouse.

It has been discovered that, by providing a novel refractory system withan improved reactant flow path for the hydrocarbon feedstock through therefractory system during the cracking, the accumulation of thermal blackon the refractory bricks can be significantly reduced or, in certaincases, substantially eliminated. This reduction leads to an increase inyield of final product and, it is contemplated, will lead to anincreased useful life for the refractory bricks and reducedcontamination of the final thermal black product.

More specifically, it has been discovered that one of the principalreasons for the accumulation of thermal black is the formation of `deadregions` in the gas flow adjacent portions of the refractory bricks.These dead regions comprise areas of reduced gas flow rate whereinthermal black may accumulate. Of course, dead regions also reduce the`active` surface area of the refractory brick which contributes to thecracking process as little or no gas flow impinges on the portion of thebrick covered by the dead region.

In conventional refractory systems, wedge-shaped refractory bricks areemployed and are stacked on their bases in spaced, alternating rows todefine the path for the gas flow. It has been discovered that asignificant dead region is formed in the gas flow adjacent the base ofthe wedge. FIG. 2 illustrates a pictorial representation of a gas flow100 around a wedge-shaped brick 104 and a resulting dead region 108which occurs in the gas flow adjacent the base of brick 104. Dead region108 forms soon after the commencement of gas flow 100 and is relativelystable. That is, once formed, dead region 108 tends to remain,preventing gas flow adjacent the base of brick 104 and allowing thermalblack produced during the make cycle to accumulate within the deadregion.

FIGS. 3a through 3l illustrate embodiments of the refractory bricksemployed in a refractory system in accordance with the presentinvention. The bricks of FIGS. 3c through 3h comprise the bricks formingthe majority of the refractory system and comprise elongate, generallycylindrical refractory bodies with one or more grooves or half-grooves(where the groove occurs at an end of the brick) formed along thelongitudinal surface thereof. The bricks of FIGS. 3a and 3b compriseelongate bodies with similar grooves, or half-grooves, formed on aradially curved surface opposite an elongate longitudinal flat surface.FIGS. 3i through 3l illustrate a series of end-bricks which arediscussed in more detail hereinbelow. Each of these bricks is formed ofan appropriate refractory material, as would be apparent to those ofskill in the art.

FIG. 4 illustrates a pictorial representation of a gas flow 200 around abrick 204 of FIGS. 3c through 3h, and a resulting dead region 208. Asshown in the Figure, the cross-section of brick 204 has been designedsuch that the cross-sectional aspect of brick 204 which is presented togas flow 200 decreases in the downstream direction from its greatestpoint 210. As is apparent from the Figure, the decreasing aspect ofbrick 204 which is presented to gas flow 200 results in gas flow 200remaining substantially adjacent the portion of brick 204 downstream ofthe maximum aspect point. This results in a dead region 208 downstreamof brick 204 which is relatively small, in comparison to dead region108.

Depending upon several factors, including characteristics of the gas,the gas flow rate, the size of the brick at point 210, and the rate atwhich the cross-section aspect decreases downstream of point 210, deadregion 208 may move, alter size and/or collapse over time.

It is contemplated that as dead region 208 is smaller, or in some casessubstantially eliminated, than is the case with prior art bricks 104,more of the surface area of brick 204 contributes to thermal transferthan is the case with the wedge-shaped brick 104. In other words, thepercentage of the brick's surface which is `active` in the crackingprocess is increased. Further, as dead region 208 is smaller, orsubstantially eliminated, the accumulation of thermal black on brick 204is reduced, or substantially eliminated.

FIG. 5a illustrates a first course of the refractory system fabricatedfrom the bricks shown in FIGS. 3a and 3b. As will be apparent to thoseof skill in the art, the majority of the course of bricks will be thoseshown in FIG. 3b but, to accommodate the curvature of the interior ofthe reactor, the shorter bricks of FIG. 3a may also be employed. To`seal` the courses of the refractory system and prevent the combustiongases and the carbon aerosol mixture from contacting refractory material22 lining the reactor chamber, end-bricks (FIGS. 3i through 3l) areplaced as shown to seal the perimeter of each course.

FIG. 5b illustrates a partial second course of the cylindrical bricks ofFIGS. 3c through 3h being laid with the round underside of thecylindrical bricks mating with the grooves, and pairs of half-grooves,of the upper surfaces of the bricks of the first course which are laidperpendicular to the course above. Again, as would be apparent to thoseof skill in the art, where necessary an end-brick (one of those shown inFIGS. 3i through 3l as appropriate) would be included to seal theperimeter of the second course.

Each subsequent course of the refractory system would be laid,perpendicular to the course below, using the cylindrical bricks of FIGS.3c through 3h wherein the round underside of the bricks of one coursemate to the grooves and half-grooves of the course below. The top courseis preferably principally formed with the bricks of FIGS. 3c through 3e,as appropriate, wherein the bricks are laid inverted such that thegrooves and half grooves of the bricks in the top course engage thegrooves and half grooves of the course below. Of course, the top courseis also formed with the appropriate end bricks to provide the desired`seal`.

FIGS. 6 and 7 illustrate a portion of several courses of the refractorysystem with the end-bricks (hatched) in place. As apparent from FIGS. 6and 7, there are no flue openings in the stack of courses i.e. onelooking downward on the stack would not be able to see through thestack. FIG. 8 illustrates a top view of a cross section of the completedrefractory system in a reactor, with the top course being shown to theright of line 9--9 and the course below being shown to the left of line9--9. FIG. 9 illustrates a side cut-away view of the refractory systemin the reactor of FIG. 8. As can clearly be seen in these Figures, thespaces between each of the parallel refractory bricks of each course,and the spaces between each course, define a tortuous path for the gasflow.

While the present invention provides a refractory system which reducesaccumulated thermal black on the refractory bricks and increases thepercentage of active surface of the refractory bricks, it is alsocontemplated that the invention provides an additional benefit in that arefractory system, including grooved bricks according to the presentinvention, may be relatively easily and simply constructed through theengagement of the grooves with the bricks of the course above or below,thus reducing the time and labour requirements for re-bricking areactor.

As shown in FIG. 4, the preferred embodiment of the present inventionincludes a refractory brick with a circular cross section. It iscontemplated however, that refractory bricks of other cross-sections mayalso be employed provided that the cross-section of the brick has beendesigned such that the cross-sectional aspect of the brick which ispresented to the gas flow decreases, in the downstream direction, from amaximum aspect presented to the gas flow. As mentioned above, thisdecrease promotes the gas flow to remain substantially adjacent thebrick downstream of the maximum aspect point. For example, FIG. 10illustrates a cross-section of a refractory brick for use with thepresent invention wherein the brick has an elliptical cross-section witha maximum aspect indicated at 240, the aspect decreasing downstreamrelative to the gas flow.

FIG. 11 illustrates another refractory brick for use with the presentinvention wherein the brick has a `tear-drop` shaped cross-section witha maximum aspect indicated at 260, the aspect decreasing in thedownstream direction of the gas flow.

While the previous exemplary cross-sectional shapes of the bricks havesmoothly decreased their aspect from the maximum aspect point, thepresent invention is not limited to such shapes. FIG. 12 illustratesanother contemplated refractory brick for use with the present inventionwherein a brick with a polyhedron shaped cross-section is employed andagain, the brick presents a maximum aspect at point 280, the aspectdecreasing in the downstream direction, albeit not smoothly. In thisparticular example, a brick with a twenty-four sided cross-section isemployed however, as will be apparent, the actual number of sides is notparticularly limited provided that the number is selected such that thegas flow is maintained substantially adjacent the brick downstream ofthe maximum aspect point.

It will be apparent to those of skill in the art that the primaryconsideration in selecting the cross-section of refractory bricks foruse with the present invention is that the cross-section should resultin reduced dead regions in the gas flow travelling through therefractory system. Of course, it is also important that it be possibleto construct a refractory system which is mechanically stable andrelatively easily constructed.

For example, it may be the case that the tear-drop shaped brick of FIG.11 is better suited to providing the desired flow characteristics than abrick of circular cross-section but it is contemplated that it may notbe cost-effective to mechanically construct a large refractory systemfrom bricks of this shape. Of course, if the improvement in yield andother economic operating characteristics merits it, the cost ofconstructing a refractory system employing elliptical or tear-dropshaped bricks may still be justified and it is not intended to excludesuch embodiments from the scope of present invention.

What is claimed is:
 1. A method for producing carbon black in arefractory system, comprising the steps of:arranging in the refractorysystem a plurality of refractory bricks, each brick having an elongateaxis, to provide at least one path through which a gas can flow, said atleast one path extending substantially perpendicular to the brickelongate axes, and each of said plurality of refractory bricks having across-section for reducing the formation of dead regions in said gasflow adjacent said bricks, each brick cross-section having a width whichdecreases in a downstream direction with respect to the gas flow toreduce the dead regions, said plurality of refractory bricks beingdisposed in at least three courses such that bricks of a first courseare staggered with respect to bricks of the third course, bricks of thesecond course being disposed at an angle with respect to bricks of thefirst course, the three courses presenting an aspect to said gas flowwhich is substantially free of flue openings on an inside of the coursesof bricks; heating the refractory system; introducing a feedstock gasflow to said path to cause production of carbon aerosol comprisingcarbon black; and removing the carbon black from the carbon aerosol. 2.A method according to claim 1, wherein said heating step comprises thestep of heating the plurality of refractory bricks to a temperature ofat least 2400° F.
 3. A method according to claim 1, further comprisingthe step of halting the heating step prior to the introducing step.
 4. Amethod according to claim 1, wherein said introducing step causesproduction of carbon aerosol comprising carbon black and hydrogen gas,and further comprising the step of heating a parallel refractory systemwith said hydrogen gas.
 5. A method according to claim 1, wherein saidarranging step comprises the step of arranging the plurality ofrefractory bricks such that the elongate axes of the refractory bricksof said first course are substantially perpendicular to the elongateaxes of the refractory bricks of said second course.
 6. A methodaccording to claim 1, wherein said arranging step includes the step ofproviding a plurality of end-bricks to respective ends of the first,second, and third courses of bricks to seal the perimeter of each ofsaid first, second, and third courses of bricks to substantially preventgas flow therethrough.
 7. A method according to claim 1, wherein saidarranging step comprises the step of arranging the plurality ofrefractory bricks such that the cross-section of each brick decreasessmoothly in a downstream direction from a maximum width.
 8. A method forproducing carbon black in a refractory system, comprising the stepsof:arranging in the refractory system a first course of refractorybricks disposed substantially parallel to each other and spaced apart topermit gas to flow through said first course in a direction orthogonalthereto; arranging in the refractory system a second course ofrefractory bricks disposed over said first course, said second course ofrefractory bricks being disposed substantially parallel to each otherand spaced apart to permit the gas to flow through said second course ina direction orthogonal thereto; arranging in the refractory system athird course of refractory bricks disposed over said second course andbeing staggered with respect to the first course of refractory bricks,said third course of refractory bricks being disposed substantiallyparallel to each other and spaced apart to permit the gas to flowthrough said third course in a direction orthogonal thereto, theinterior of the three courses of refractory bricks being disposed topresent an aspect to the gas flow which is substantially free of flueopenings, each brick of said first, second, and third courses having across-section with a width which decreases in a downstream directionwith respect to the gas flow to reduce the formation of dead regionsadjacent said each brick; heating the refractory system; introducing afeedstock gas flow to said first, second, and third courses of bricks insaid orthogonal direction to cause production of carbon aerosolcomprising carbon black; and removing the carbon black from the carbonaerosol.
 9. A method according to claim 8, wherein said introducing stepis stopped when the temperature of said refractory system falls below anoperating temperature within the range of substantially 1000° F. tosubstantially 1500° F., and wherein said heating step comprises the stepof heating said refractory system to a temperature within a range ofsubstantially 2400°0 F. to substantially 2950° F.
 10. A method accordingto claim 8, wherein said carbon aerosol comprises carbon black andhydrogen gas, and further comprising the step of introducing saidhydrogen gas into a parallel refractory system to heat the bricks of theparallel refractory system.
 11. A method according to claim 8, whereineach of said arranging steps includes the step of arranging refractorybricks such that each brick has a substantially oval cross-section. 12.A method according to claim 8, wherein each of said arranging stepscomprises the step of arranging refractory bricks such that each brickhas a substantially circular cross-section.
 13. A method according toclaim 8, wherein the second arranging step comprises the step ofarranging the second course of refractory bricks such that theirelongate axes are substantially perpendicular to elongate axes of thefirst course of refractory bricks.
 14. A method according to claim 8,further comprising the step of arranging a plurality of end bricks atrespective ends of said first, second, and third courses of refractorybricks to substantially prevent gas flow therethrough.
 15. A method ofusing an array of refractory bricks in a reactor to produce carbonblack, comprising the steps of:disposing in the refractory system aplurality of refractory bricks, each having an elongate axis, to provideat least one path through which a gas can flow, said at least one pathextending substantially perpendicular to the brick elongate axes, eachof said plurality of refractory bricks having a cross-section with awidth which decreases in a downstream direction with respect to the gasflow to reduce the formation of dead regions adjacent said bricks, saidplurality of refractory bricks being disposed in at least three coursessuch that bricks of a first course are staggered with respect to bricksof the third course, bricks of the second course being disposed at anangle with respect to bricks of the first course, an interior of thethree courses presenting an aspect to the gas flow which issubstantially free of flue openings; disposing in the refractory systema plurality of end-bricks at ends of said first and second courses toseal a perimeter of said array to substantially prevent gas flow throughthe ends of the first and second courses; heating the refractory system;introducing a feedstock gas flow to said path to cause production ofcarbon aerosol comprising thermal black and hydrogen gas; and removingthe thermal black from the carbon aerosol.
 16. A method according toclaim 15, wherein the first disposing step comprises the step ofdisposing refractory bricks each having a cross-section which decreasessmoothly in a downstream direction from a maximum width.
 17. A methodaccording to claim 16, wherein the first disposing step comprises thestep of disposing refractory bricks each having a cross-section which issubstantially circular.
 18. A method according to claim 16, wherein thefirst disposing step comprises the step of disposing refractory brickseach having a cross-section that is substantially oval.
 19. A methodaccording to claim 15, further comprising the step of disposing a meansfor engaging at least one brick of said first course with a least onebrick of said second course.
 20. A method according to claim 19, whereinthe first disposing step includes the step of engaging a groove of saidat least one brick of said second course with said at least onerefractory brick of said first course.